Introduction: Large Bore Vacuum Cannon

In this project I'll be building a 4 inch bore vacuum cannon. This sort of cannon can fire large projectiles at high speed, and requires no explosive fuel or compressed air tanks to do so. Instead, the weight of Earth's own atmosphere is the force responsible for accelerating the projectile. With a vacuum pulled inside the cannon, breaking a seal on one end is like blowing the hatch on a submarine while it's still under water. Air explosively fills the barrel, pushing any object in it's way until the momentum of those objects is great enough to punch through the other end.

Be sure to watch the video tutorial/demonstration embedded at the top of this page, and written instructions will be included in the following steps.

Parts/items required for the cannon:

  • 4" PVC pipe
  • Brass hose barb
  • Vacuum pump
  • Aluminum foil
  • Duct tape
  • 3" PVC end caps (ammunition)

Parts required for the stand:

  • 2x4
  • Wood screws
  • Large zip ties

Step 1: Cannon Assembly

Because there is no valve or combustion chamber required, the design of a vacuum cannon can be very simplistic. Mine was made from a 10 foot long, 4 inch diameter section of PVC pipe (sch.40, pressure rated). After covering a portion of the ends so that there will be a nice clean surface that I can later make a seal against I gave the pipe a coat of paint.

About 6" from one end two holes are drilled, just barely large enough to thread in brass fittings for attaching vacuum lines. I will be using two separate pumps to make drawing a vacuum inside the cannon a faster process, but one is adequate to get the job done. If using only one vacuum pump only one hole and fitting is necessary.

One nice thing about working with PVC is that it's soft enough for metal threads to carve their way through the plastic, which usually results in a perfect seal with no need for a tap and die kit. If the fittings end up leaking (possibly due to an incorrectly drilled hole) they can be removed and wrapped with teflon thread tape and screwed back in place.

Step 2: Building the Stand & Mounting the Cannon

To keep the cannon from rolling around I threw together a simple wood base made from a 2x4. Three pairs of holes are drilled along the length of this base for tethers to be inserted that will secure the cannon. After painting the stand I inserted large zip ties through the pre-drilled holes and set the cannon on top. I found the three sets of zip ties to be enough to hold the cannon securely, though I did have one snap after about 20 shots.

Step 3: Finishing the Cannon Ends

With the cannon secured I can expose the ends. For this piece of pipe to properly hold a vacuum, the edges of the cut ends need to be rounded over and sanded very smooth. Rough sanding was done with a flap disc on an angle grinder, then finer grits of sandpaper were used by hand.

Step 4: Burst Discs

A vacuum cannon uses what is called a burst disc on both ends. The purpose of a burst disc is to be strong enough to hold pressure while the cannon is being emptied of air, but weak enough they they will burst when ruptured manually.

In this case the discs are made of four layers of heavy aluminum foil, roughly cut into a circle and pressed with a 4" coupling over the end of the pipe to properly form them into shape. The coupling is only temporary, to help pull the foil tight and fold the edges over. To hold the burst discs in place while the cannon is used the foil is secured with duct tape.

Step 5: Vacuum Pumps

As I mentioned in an earlier step I am using two vacuum pumps with this cannon.

One is an inexpensive electric pump that I purchased online, and it does an ok job of drawing a weak vacuum quickly, but it really slows down once it has to work harder to get the last bit of air out. The strength of a vacuum uses a unit of measurement called inches of mercury, with 30 inches being about the maximum that is possible under Earth's atmosphere. At around 15 inches I start using a manual high volume vacuum pump that I built myself in a project several years ago (seen here). This manual pump is hard work, but it does a great job pulling a strong vacuum when electric pumps tend to give out.

Step 6: Firing the Cannon

My first tests with this cannon were with no projectile loaded, and only a single layer of foil acting as the burst disc on either end. In the project video you can see a clip where one of these single layer burst discs ruptures all on it's own as it cannot withstand the pressure. I found that four layers made for the best reliability.

Even with the proper amount of foil it's important never to stand in front of, or directly behind a vacuum cannon that is under pressure. It doesn't take much for a burst disc to rupture by accident, and the cannon could potentially fire backwards if the forward disc were to rupture first.

The steps for firing this cannon are to first load a projectile (in my case a 3" end cap), then form and secure a burst disc to both open ends of the pipe. The vacuum pumps are then used to pull anywhere between 24-30in/hg of vacuum within the cannon, and when ready, a hammer ruptures the rear disc to send the projectile flying.

I hope you've enjoyed this project, and remember to check out the full video to see the cannon in use!

Comments

author
N6OZG made it!(author)2017-03-14

How about adding a large pressure chamber behind the rupture disk? Increasing the pressure until the rupture disk fails should up the velocity of the projectile.

author
lurifax made it!(author)2017-03-10

And this is the exact same reason that the Hyperloop will never be a viable mean of transportation. Imagine being in a capsule and the hyperloop leaks anywhere behind you. Your capsule will be that projectile.

Cool project, I remember doing this is physics class as a kid. :-)

author
RicksterInstructables made it!(author)2017-03-10

I think they realized that there would be zero chance that they could build it without leaks.

And pulling a vacuum in a tube that size of any length would take basically to infinity.

The latest plans I saw for the hyperloop had it "relying" on only a "subtle" vacuum.

Because Elon Musk is a well respected visionary, I won't tell you what my spell check did to "hyperloop."

author
+Oncer made it!(author)2017-03-10

I love the fact that you put the watermelon back together for the second shot! Waste not want not.

Great 'ible though not sure why I would need one other than for the hell of it.

author
Laral made it!(author)2017-03-09

WOW! Now this is my kind of project. Utter simplicity. Based on an understanding of physics. Lets nature do most of the work. Even gives you a good workout. Kudos!

I'm wondering… Those rings you use to shape the foil—could they be tight enough to just leave on, without having to tape at all?

Also, I think you could make a simple piercing device that you could trigger from a distance with a simple trip cord or wire.

author
astrong0 made it!(author)2017-03-09

I think a small rocket shaped projectile needs to be created and this needs to be either launched straight up or at a 45 degree angle.

author
diy_bloke made it!(author)2017-03-09

Great stuff. For a moment (seeing the prime picture) I thought you were shooting watermelons as ammo :-)
What you guess is the penetration rate in zombies?

author
2905 made it!(author)2017-03-09

How far will the projectile travel?

author
Altoidian made it!(author)2017-03-09

I jsut love this kind of stuff. I'm a ballistics nut, anyway. Enjoyed your Instructable. Nice!

author
lfoss made it!(author)2017-03-09

Interesting!! Not quite as portable as my AR-15 or 12 gauge shotgun though! =P

author
CalebGreer made it!(author)2017-03-09

"Watches cannon

*Chuckles evilly*"

Nice work :)

author
kooth made it!(author)2017-03-08

Very cool! Thanks for posting!

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Bio: I like turning boring things into awesome things! Usually on video.
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